Objective:
The long-term goal of this research is to improve the understanding of the fate and transport of veterinary antibiotics, antibiotic-resistant bacteria, and resistance genes in soil, surface runoff, and tile-drained water to surface water in agricultural watersheds. Specific objectives are to: 1) Determine the losses of antibiotics from manured fields in runoff water, tile drainage, and water leaching to groundwater; 2) Determine the concurrent losses of antibiotic-resistant bacteria (Enterococcus, a fecal indicator and opportunistic pathogens) and antibiotic-resistance genes from manured fields in runoff water, tile drainage, and water leaching to groundwater; and 3) Evaluate and improve the capabilities of the Root Zone Water Quality Model to predict losses of antibiotics.

Approach:
Losses of antibiotics and antibiotic resistant bacteria will be determined in runoff and tile drainage at existing field sites near Ames, Iowa, Nashua, Iowa, and Platteville, Wisconsin, which receive chicken, swine, and beef manure, respectively. The antibiotics, tylosin, tetracycline, and sulfamethazine are the focus of the study, and these will be measured in soil and water by extraction and HPLC-MS/MS or ELISA (tetracycline). Antibiotic-resistance will be assessed by measuring antibiotic-resistance genes relevant to the focus antibiotics using qPCR methods. In addition, total and antibiotic-resistant Enterococcus will also be measured using cultural methods. In addition to the field monitoring studies, rainfall simulations will be conducted after manure application to facilitate modeling of contaminants by macropore transport. The persistence and transport of antibiotics will be modeled using the Root Zone Water Quality Model (RZWQM). The simulated rainfall experiments will provide the data for model calibration, allowing modeling of the field site data.